If you have a damaged tub chair then you have three choices. The first is to get rid of it and buy a new one. The second is to get someone to repair it, and the third is to repair it yourself. The first option is the most expensive unless you can find a really cheap tub chair from a second hand store.
Getting a specialist to repair it will also cost quite a bit of cash, and it will all depend on how damaged it is. If it is just cosmetic then a re-cover should do the trick. This involves stripping away the old fabric and replacing it with new. The result is a chair that looks brand new. Repairing it yourself if the cheapest option, but you really need to know what you are doing before you start.